1. Field of the Invention
This invention relates to an information recording method and an optical recording medium. More particularly, it relates to an information recording method and an optical recording medium in which secondary or subsidiary signals are prerecorded on a recording track by offsetting the track in a direction parallel to the track width. More particularly still, it relates to an information recording method and an optical recording medium in which the adverse effects which the signals produced by this offsetting of the recording track might have on the main signals recorded on the recording track are eliminated.
2. Description of the Prior Art
It is known in the prior art to form a guide groove or pregroove or grooves in a spiral or concentric pattern on an optical recording medium, such as a magneto-optical disc, and to record or reproduce data on or from a recording track along the track length, using the photomagnetic effect, which recording track coincides with the previously formed guide groove or pregroove or the land between the grooves.
Specifically, it is known to record data and control information, such as sync signals or addresses, on the recording track alternately and to perform data control on the basis of the control information. It is with the aid of the control information that the data are recorded or reproduced on a block-by-block or sector-by-sector basis.
Japanese patent publication No. 63-87682/1988 discloses a technique in which a wobbling track for detecting tracking errors is recorded after frequency modulation by a time code. With this technique, a sinusoidal carrier signal having a frequency of, for example, 22.05 kHz is frequency modulated by a time code signal of a frequency which is low enough as compared to that of the carrier to form the wobbling track, so that, during reproduction, a tracking error signal may be produced from the wobbling track, while the time code signal is demodulated to produce a time code as position information. However, with this prior art technique, clocking of the signals recorded on the track cannot be achieved with the track wobbling signal. A unit of time information data at most may be inserted in one block with the wobbling signal, and this reduces the extraction accuracy. In addition, decoding cannot be achieved unless one complete block is read out so that correct position matching cannot be achieved without difficulty.
In order to reproduce the main information recorded on the recording track along the track length, in the form for example of magneto-optical signals or Mo signals, it is known to provide a long preamble region for clock reproduction or clocking at the leading end of the main information and to extract clocks for reproducing the MO signals from the signals written in the preamble region. However, the data recording capacity is decreased in this case by an amount corresponding to the length of the preamble region.
To overcome these problems, the present inventors have already proposed a method which consists in pre-recording the control information, such as frame sync signals or addresses, by offsetting the recording track along its width (i.e., in a direction parallel to its width), reproducing the control information, and using the reproduced control information as frame sync signals or addresses for recording or reproducing the main signals or main information. The present inventors have already proposed a method for reducing the length of the preamble region by employing the prerecorded frame sync signals in the form of track offsets along the track width as the frequency capturing signals at the PLL and using the signals recorded on the recording track for phase capture at the PLL.
Unfortunately, the signals as heretofore recorded in the form of track offsets along the track width affect the main signals recorded on the recording track. Specifically, during phase capture of the PLL, the points of transition or edges of the signals recorded in the form of track offsets along the track width may interfere with and affect the main signals recorded on the track to produce jitter in the reproduced clocks.